Since my older son was diagnosed with an autism spectrum disorder (ASD) at age 3, I read many books on autism. From those books I learnt that the chance that a sibling would also have/develop an ASD was about 5%, compared with the 1% chance for anyone in the population (that is, about 1% of children are officially diagnosed with autism, but I think one can seriously doubt whether that figure is not an underestimation due to under-diagnosis).
I always thought that this 5% figure was odd, since it didn’t correspond at all to my observation at the special-needs-daycare/school of my son or in online parent support groups or in accounts of families affected by ASDs that I read, where many parents report to have several children with an ASD. I noticed just way too many children who also had siblings with an ASD to make that figure of 5% correspond to reality. And now, there’s a study just published in Pediatrics, confirming my observation: if a parent has a child with autism, the chance of a sibling also developing an ASD is almost 20%. That’s what the authors found in a large American sample, and I don’t see any reason why it would be different for other parts of the world.
Not sure how that will change the way we look at autism (if it will make any difference at all), but I find it a striking (but not surprising) figure.